/    / 


1 


1'.  S.  DEPARTMEN1    OF   AGRICULTURE, 

BUREAU   OF    BHT0M0L0GY-  CIRCULAR   No.   172. 

I      <  >    I IOWARI  >.   I  nlomolojri.l  «nd  Oriel  ol  IW.u. 


INK  RKI>  si'IDKI!  ox  COTTON 


e.  \  McGregor, 

Entomolonii  n\ 


BUREAU  OF  ENTOMOLOGY. 

L.  O.  Howard.  Entomologist  and  Chief  of  Bureau. 

C.  L.  Mari.att,  Entomologist  and  Acting  chief  in  Absence  of  Chief. 

R.  S.  Clifton.  Executive  Assistant. 

W.  F.  Tastkt,  Chief  Clerk. 

F.  H.  Chittenden,  in  charge  of  truck  crop  and  stored  product  insect  investigation  t. 

A.  D.  Hopkins,  in  charge  of  forest  insect  investigations. 

W.  D.  Hunter,  in  charge  of  southern  field  crop  insect  investigations. 

F.  M.  Webster,  in  charge  of  cereal  <in<t  forage  insect  investigations. 

A.  L.  Qttaintance,  iu  charge  of  deciduous  fruit  insect  investigations. 

E.  F.  Phillips,  in  charge  of  bee  culture. 

D.  M.  Rogers,  in  charge  of  preventing  spread  of  moths,  field  work. 
ROLLA  P.  Currie.  in  charge  of  editorial  icork. 

Mabel  Colcord,  in  ehanje  of  library. 

Southern  Field  Crop  Insect  Investigations. 
W.  D.  Hunter,  in  charge. 

W.  D.  Pierce,  G.  D.  Smith,  J.  I).  Mitchell,  Harry  Pinkus,  B.  R,  Goad,  R    \V. 

Moreland,  A.  W.  J.  Pomerov,  engaged  in  CO  I  ton-boll   weevil  i  n  rest  if/a  t  ions. 

F.  C.  Bishopp,  A.  H.  Jennings,  H.  P.  Wood.  W.  V.  King,  engaged  in  tick  life- 
history  in  vestigations. 

A.  C.  Morgan,  G.  A.  Runner,  S.  E.  Crumb,  D.  C.  Pabman,  engaged  in  tobacco 

insect  in  vestigations. 
T.  E.  Holloway,  E.  R.  Barber,  engaged  in  sugar-cane  insect  investigations. 

E.  A.  McGregor,  W.  A.  Thomas,  engaged  in  red  spider  and  other  cotton  insect 
investigations. 

J.  L.  Webb,  engaged  in  rice  insect  investigations. 
R.  A.  Cooley,  D.  L.  Van  Dine,  A.  F.  Conradi,  collaborators. 
ii 


ADDITIONAL  COPIES  of  this  publication 
-ii-  may  be  procured  from  the  Superintend- 
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Circular  No.  172.  taoedMaj  11 

United  States  Department  of  Agriculture, 

BUREAU   OF   ENTOMOLOGY 
L.  O.   HOWARD,   Entomologist  and  Chief  of  Bureau. 


THE  BED  8PIDEB  ON  COTTON.1 

[Tetranychua  bimaculatus  Harvey.) 

By    K.    A.    Mi(i nil, 

Entomological    issittant. 

[NTHOD1  <  TION. 

The  minute  reddish  mite  commonly  know  n  as  the  red  spider  appar- 
ently i-  becoming  one  of  the  serious  enemies  of  the  cotton  planl  in 

the  United  State-.  It  i-  now  prevalent  throughout  the  cotton  licit, 
and.  especially  in  the  last  few  seasons,  has  caused  much  alarm  among 
the  fanner-  in  certain  sections.  Seasons  of  excessive  drought  arc 
favorable  to  the  development  of  the  mite,  and  at  such  time-  the  pest 
increases  90  rapidly  that  the  damage  often  becomes  severe  before  it- 
presence  i-  detected. 

Red-spider  infestation  i<  frequently  miscalled  "rust*'  by  farmers, 
since  infested  leaves  soon  turn  deep  red  on  their  upper  surface.  Such 
leave-,  however,  if  examined  underneath,  reveal  the  presence  of  the 
red  spiders  and  the  inconspicuous  webs  behind  which  they  arc  feed- 
ing and  laying  their  eggs. 

HISTORY    \M>  DISTRIBUTION. 

With  the  exception  of  an  outbreak  in  Louisiana,  reported  by  Prof. 
II.  A.  Morgan  in  L893,  severe  occurrence  of  the  red  spider  on  cotton 
had  not  been  rep.  rted  until  1903,  at  which  time  complaint-  of  dam- 
age came  from  South  Carolina  and  Georgia.      In  1904   Mr.  I-'..  S.  G 

1  This  firruinr  i*  baaed  primarily  upon  work  done  :it  Batesburg,  s  C,  in  1911  and  1912, 
under  rh.>  direction  of  Mr.  W.  l»    Banter,  bat  also  Include*  the  results  o(  uuaenal 

<;.  a.  Runner  and  11    f.  Wilson  daring  the  two  preceding  seasons,     it    - 
»f  and  ■opersedes  Circular  No.  !■"". 

1 


THE    RED    SPIDER    OX    COTTON. 


Tit  id-,  then  of  this  bureau,  found  severe  infestation  in  fields  about 
Batesburg,  S.  C,  and  the  following  year  he  reported  severe  injury 
in  North  Carolina.  South  Carolina.  Georgia,  and  Alabama.  Since 
then  the  additional  records  of  Dr.  F.  II.  Chittenden  and  Messrs. 
G.  P.  Weldon,  D.  T.  Fullaway,  and  others,  as  well  as  the  writer. 
have  established  the  presence  of  this  red  spider  from  Maine  to  Flor- 
ida and  westward  to  California  and  in  the  Hawaiian  Islands.  With 
the  exception  of  western  Colorado  and  portion-  of  California  no 
complaints  of  an  alarming  nature  regarding  this  pest  have  come  to 

the  writer's  attention  other  than  from 
the  southeastern  portion  of  the  cotton 
belt.  It  is  here  that  the  red  spider  ap- 
pears to  have  found  the  conditions  most 
suitable  for  its  development. 

The  red  spider  was  described  by  Har- 
vey in  1893  as  Tetranychua  2-maculatu8. 
Harvey  considered  it  quite  distinct  from 
the  European  species  T.  telarius  L.  His 
types  were  from  Orono.  Me.  In  11)07 
Prof.  H.  A.  Morgan  published  observa- 
tions on  the  cotton  mite,  and  apparently 
accepted  the  determination  of  the  species 
as  T.  telarius.  In  1D00  Mr.  Nathan  Banks 
described  the  cotton  mite  under  a  dis- 
tinct name — Tetranychua  gloveri — but 
from  the  study  of  additional  specimens 
has  now  concluded  that  the  name  is 
synonymous  with  Harvey's  T.  bimacu- 
latus.  Specimens  of  red  spiders  on  cotton 
from  South  Carolina  have  upon  two  re- 
cent occasions  been  determined  by  Prof. 
A.  Berlese  as  the  continental  specie: — 
Tetranychua  telarius.  As  there  seems  to 
be  considerable  doubt  on  this  point,  we  shall  follow  Mr.  Banks 
in  considering  the  form  with  which  we  are  dealing  as  Tetranychua 
bimaculatus. 

DESCRIPTION. 

The  typical  female  (fig.  1)  is  0.50  mm.  long  by  0.26  mm.  wide. 
broad-oval,  widest  in  front,  and  the  legs  are  shorter  than  the  body. 
Its  color  is  usually  brick-red.  The  typical  male  is  0.27  nun.  long  by 
0.1.")  mm.  wide,  oval-wedge  shape,  narrowed  behind,  the  legs  about 
equaling  the  length  of  the  body,  and  its  color  i-  usually  reddish 
amber.  Individuals  of  both  sexes  usually  possess  on  either  side  of 
the  body  a  dark  spot,  caused  by  the  food  contents.  This  -pot  may 
vary  greatly  in  color,  size,  and  outline.     Similarly,  depending  upon 


Fig.  i.  The  red  spider,  Tetrany- 
rlnis  Mmaculatus:  Adult  fe- 
male G  r  e  a  t  1  y  enlarged. 
i  From  Banks,  i 


I  ill     i;i  D    BFIDI  R  ON   COTTON.  •'. 

the  host  plunl  and  upon  locality,  the  general  color  of  the  red  spider 
i-  subject  i  o  great  *  ariat  ion. 

I'lu'  egg    are  ven  minul  ■.  but  in  proportion  to  the  mites  the}  are 
large.     1 1  n- \  are  perfectly  round,  and  when  first  laid  are  as  cleai    i 
water.     Bach  female  lays  (in  the  months  of  June,  July,  and  August) 

about  .'in  to  60  eggs,  although   her  br I  may  in  cases  exceed    100, 

[Tsualh  about  G  i^^-  are  deposited  \»y  da}  for  a  period  of  fl  or  10 
days.  Less  than  •'•  eggs  or  more  than  I"  are  rarely  deposited  in  one 
day  in  summer  weather.  During  the  warmer  months  the  eggs  hatch 
in  about  I  daj  -  a  fter  being  laid. 

The  newly  hatched  red  spider,  called  the  larva,  is  almost  round, 
has  six  legs,  and  is  nearh  colorless.  Ii  begins  feeding  at  once,  and 
i  in  summer  time)  after  two  days1  activity  it  becomes  quiet,  darkens 
in  color,  casts  its  skin  for  the  first  time,  and  emerges  as  the  primary 
nymph  \\  ith  an  added  pair  of  legs     making  eight. 

The  primary  nymph  becomes  larger  in  size  and  darker  in  color, 
I  ii  it  gives  no  indication  of  sex.  Feeding  continues  actively,  and  at  the 
termination  of  another  two-day  period  i  in  summer  months)  :•  second 
molting  occurs,  which  gives  rise  to  the  third  stage  the  secondary 
nymph. 

With  this  last  nymphal  stage  the  first  indication  of  sex  appears. 
As  with  the  preceding  stages,  two  days  usually  suffice  in  summer 
for  the  completion  of  this  period,  at  the  end  of  which  time  the 
skin  is  shed   for  the  third  time  and  at   last   the  perfectly  developed 

adult  mill'-  appear.    Ai  il :currence  of  each  molt  the  skin  splits  in 

two,  crosswise,  and  tin-  creature  crawls  out  of  the  two  halves.  The 
old  cast  skins  are  usually  t<>  be  seen  in  abundance  among  the  fibrils 
of  the  \\  eb. 

I  III      \DI   M     \I  \I  l  -     \\n    FEMALES    COMPARED. 

Concerning  the  relative  abundance  of  females  and  males  it  may  !>»■ 
said  that  there  seems  to  be  n  predominance  of  females  throughout 
the  summer,  but  toward  the  approach  of  cold  weather  the  occurrence 
of  the  sexes  becomes  more  nearly  equal.  The  period  of  life  of  the 
.•idult  female  varies  from  1"  tiny-  in  midsummer  to  several  months 
in  winter.  The  male  is  shorter  lived.  A-  before  stated,  the  female 
i-  decidedly  larger  than  the  male,  more  rounded  behind,  and  of  a 
much  deeper  color.  She  does  n< >t  move  about  much,  and  when  she 
■  loo-  her  motion  is  rut  I  in-  slow.  <  hi  the  other  hand,  when  not  mating, 
the  male  is  frequently  seen  moving  rapidly  about.  The  body  and 
legs  are  well  beset  with  bristles,  which  are  -"mew  hat  more  con 
spicuous  in  the  male-  than  in  the  females.  In  addition,  the  legs  of 
the  male  are  longer  in  proportion  to  the  body  than  are  those  of  the 
female.  The  legs  of  the  first  pair  are  especially  long  in  the  male,  and 
are  doubtless  adapted  for  clasping.  The  ey<  -.  consisting  ea<  h  of  two 
orbs,  one  close  behind  the  other,  are  situated  near  the  front  edge  of 
the  body  directly  over  the  second  pair  of  legs. 


THE   RED   SPIDER   ON    COTTON. 


MATIXO. 


Almost  immediately  upon  becoming  adult,  the  red  spiders  mate 
and  begin  egg  laying.  The  males  seem  to  recognize  unfertilized 
females  with  ease.  The  first  eggs  are  frequently  deposited  on  the 
same  day  upon  which  the  transformation  occurs  from  the  last 
nymphal  to  the  adult  stage. 

PARTHENOGENESIS. 

Experiments  conducted  with  unmated  female  red  spiders  clearly 
prove  that  they  are  normally  capable  of  laying  eggs,  which  in  turn 
hatch  and  develop  into  mature  individuals.  Xo  tests,  however,  have 
been  successfully  conducted  to  determine  the  sexual  fertility  of  the 
latter. 

GENERATIONS. 

The  season  of  1911  at  Batesburg,  S.  C,  was  one  of  unusual  drought 
and  heat,  and  there  were  about  IT  generations  between  March  11  and 
November  5.  The  time  required  for  a  single  generation  varied  from 
35  days  in  March  and  early  April  to  10  days  throughout  most  of 
.Tune,  July,  and  August,  and  to  25  days  in  the  greater  portion  of 
October  and  early  November.  During  the  same  period  of  1912  at 
Batesburg  only  1G  generations  were  produced.  The  1912  season 
was  late  in  commencing,  was  somewhat  cooler  than  that  of  1911,  and 
more  showers  occurred.  From  April  24  to  September  25  there  was 
small  variation  in  the  time  required  for  the  generations — averaging 
about  11  days.  Two  generations  developed  each  in  9  days,  which  is 
less  than  was  required  for  any  brood  in  1911.  Thirty  days  was  re- 
quired for  the  October-November  generation.  The  following  table 
presents  the  duration  of  each  stage  of  each  of  the  17  generations 
for  1911 : 

Table  I. — Development  of  veneration*  of  tin-  nil  spider  on  cotton  in  1911. 


Gener- 
ation. 


Period  covered  by  generation. 


Incuba- 
tion 
period. 

Larval 
period. 

Nvmph 

"(1) 
period. 

Days. 

Days. 

Days. 

13 

9 

6 

6 

3 

3 

6 

3 

3 

5 

3 

2 

5 

3 

2 

4.5 

2.5 

2 

4 

2 

2 

4 

•> 

2 

4 

2.5 

2.5 

4 

2 

2 

4 

2 

2 

4 

2 

) 

5 

2.5 

■> 

5 

2 

2 

5 

3.5 

3 

>; 

A 

A 

9 

6 

5 

5.5 

3.1 

2.7 

Xymph      Ovipo- 
i2i         sit  ion  to 
period.        adult. 


1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 


Mar.  11  to  Apr.  14. 
Apr.  15 to  Apr. 29. 
Apr.  30  to  Mav  13. 
Mav  11  to  May.'.",.. 
May  26  to  June  6.. 
June  7  to  June  17.. 
June  is  to  June 27. 
June  28  to  July  7.. 
July  8  to  July  18.. 
July  19  to  July  28. 
July  29  to  Auj;.  7.. 
lug.  B  lo  Aug.  1 , .. 
Aug.  is  to  Aug.  29. 
A.ug.30toSept.9. 
Sept.  10  to  Sept.  24 
Sept.  25  to  Oct.  io. 

Oct.  11  to  Nov.  4.. 
\verage 


Days. 


2 

2 

2 

2 

2 

2 

2 

2 

2 

2.5 

2 

3.  a 

4 

5 


Days. 


35 
15 
14 
12 
12 
11 
10 
10 
11 
10 
10 
10 
12 
11 
15 
16 
26 


2.8 


I  ii  I     Kin   BPID1  i:    ON    '  01  l<>\".  5 

le  1 1  indicates  the  duration  of,  and  the  period  covered  by,  each 
of  tlir  it,  generations  for  1912  ;i-  well  at  for  the  1911    12  wintering 
era I  ion. 

I.I      ||  /  I,   l  i  h, /il, 1 1  ill    ,,! :    il'   Hi  l  H  I  I'm  -  .■•     ./hWi   ,     .,</     i  nl  Inn     in     I''!   ' 


M 

ia 
ta 

ii 
ii 
i  a 
i-' 
ii 

Hon 

\n      1   191]    to  \ 

\i>r 

in 

■ 

0 

10 

i 

ia 

17 

■ 

1   to  Jill  \    1  1 

Jul'   IS  to  Jul \  .'I 

■  *  Intering  nil  itaoold  I 

km   \iin\    OP   w  I   v  1  ill  1 :    I"   BREEDING    \'   ITVITIES. 

The  influence  of  the  weather  on  breeding  activity  is  ven  notice- 
able. Hot,  dry  conditions  greatlj  favor  and  hasten  development, 
while  cool,  wet  weather  correspondingly  retards  it.  A  female  laying 
normally  about  6  or  7  eggs  per  day  will  often  upon  the  occurrence 
of  .i  very  hoi  day  suddenly  increase  the  number  to  15  or  even  more 
eggs  per  day,  or  upon  a  chilly  day  may  drop  ;i-  suddenly  to  1  or  -1 
Ii  i>  easy  then  to  understand  the  remarkable  rate  al  which 
this  pest  increases  during  times  of  unusual  drought. 

OBSERVATIONS   on     HABITS. 


Iii  establishing  herself  upon  cotton  the  female  selects  a  concave 
area  between  the  under  veins  of  the  leaf  and  begins  ;it  once  to  deposil 
eggs.  These  may  be  attached  to  the  fibrils  of  the  web  slightly  above 
ilic  surface,  or,  as  seems  mosl  often  the  case,  they  are  placed  directly 
upon  the  leaf.  The  eggs  are  usually  clustered  rather  closely  and 
rarely  occupy  an  area  greater  in  size  than  that  of  a  dime.  Feeding 
continues  interruptedly  throughout  the  period  of  egg  laying,  and  the 
affected  area  of  the  leaf  becomes  thickly  dotted  with  the  blackish- 
green  puncture  marks.  Meanwhile  ;i  wine-red  spol  has  appeared  on 
the  upper  surface  of  the  leaf  directly  over  the  young  colony,  which 
spreads  ;i-  the  colony  increases  and  may  finally  color  the  entire  leaf. 
A>  the  eggs  hatch  the  larva?  remain  close  to  the  place  of  their  birth. 
The  mites  seem  to  U-  decidedlj  gregarious.  In  n  young  colony 
there  is  usually  little  web  formed,  bul  where  the  spiders  are  veri 
abundant  the  web  may  become  quite  conspicuous.  It  doubtless 
affords  some  protection  from  adverse  weather  conditions,  as  well  ib 
.i ir:i : n-t    hostile  intruder-,  since   upon   several   occasions   predaceous 


THE    RED    SPIDER    ON    COTTON. 


insects  have  been  observed  ensnared  and  dead  among  the  fibers.  New 
females,  after  mating,  either  select  an  attractive  --pot  on  the  leaf, 
or  migrate  upward  to  a  more  tempting  leaf,  or,  as  frequently  is  the 
case  when  overcrowded,  travel  to  another  plant. 


THE  VIOLET  AND  POKEWEED  AS   HOSTS. 

When  cotton  dies  or  becomes  un  tempting  in  the  late  fall  an  exodus 
of  red  spiders  from  the  cotton  fields  occur-  in  the  effort  to  find  more 
suitable  food  plants.  At  this  time  cotton  mites  may  be  easily  found 
on  a  number  of  native  and  cultivated  plant-,  prominent  among  which 
are  cowpeas,  tomato.  Jamestown  weed,  ironweed,  pokeweed,  and  cul- 
tivated violets.  Most  of  these  plant-  die  after  the  frosts,  but  poke- 
weed   furnishes  considerable  green  tissue  beneath  the  ground   level. 

and  the  violet  remains  somewhat  green 
throughout  the  winter.  Out  of  many 
case-  of  cotton  infestation  investigated 
during  tin-  last  two  seasons  the  rast 
majority  of  them  have  indicated 
most  clearly  that  the  original  source 
of  the  pest  was  either  the  English 
violet  (figs.  •_'.  3)  or  pokeweed  [Phyto- 
lacca <1(  candra)   (fi<r.  4). 

Practically  all  occurrences  in  urban 
localities  have  been  intimately  associ- 
ated  with  cultivated  violet  plants  and 
doubtless  originated  from  them.  On  the 
other  hand,  with  very  few  exceptions 
rural  case-  of  infestation  are  traceable 
to  pokeweed  -talks  growing  at  the 
field  borders  or  on  the  terraces.  The 
description  of  a  rural  occurrence  at 
Allendale.  S.  C.  will  serve  to  illustrate  a  typical  case  of  origin  from 
pokeweed.  In  this  instance  the  infestation  was  seen  to  grow  increas- 
ingly severe  as  one  approached  a  certain  point  on  a  terrace.  Con- 
verging from  all  directions  toward  this  center,  infestation  clearly 
became  heavier  until  an  area  was  reached  where  the  plants  were  de- 
nuded of  foliage.  Precisely  in  the  center  of  this  area  there  grew  a 
large  pokeweed  stalk.  It  was  "alive"  with  mites  and  was  lightly 
festooned  with  their  webbing. 

It  is  not  yet  entirely  clear  in  what  maimer  the  red  spider  passes 
the  winter  on  pokeweed.  The  plant  i-  a  perennial,  and  the  stalk-  die 
to  the  ground  in  the  late  fall.  Just  below  the  soil  surface,  however, 
the  soft  fleshy  roots,  which  are  succulent,  begin  (fig.  4).  In  addition, 
at  the  crown  of  the  root,  at  about  the  ground  level,  there  are  always 


::  -i-V:  ':■■;■':: 

o  0   O  O   0 

0  o 

o 

•  □ 

Fig.  2. — Diagram  showing  how  vio- 
lets growing  in  dooryard  give 
rise  to  red-spider  infestation  in 
adjoining  field.  The  infestation 
is  most  severe  near  tli"  yard. 
This  diagram  is  typical  of  many 
cases  found  during  1011.  (Au- 
thor's illustration,  i 


I  11  I.    Ill  l>    -.  I  •  1 1  •  i  I:    i'\    COTTON. 


to  be  found  through  the  winter  months  the  tender  dormant   bud.s 
which  give  rise  t<>  the  stalks  of  the  following  season.     Upon  Novem- 
ber 23,  1912,  following  -«-\ **t;i I  severe  fro  ts  al    Batesburg,  S    I 
few  uf  the  mites  were  seen,  apparently   feeding  on  these  winter  buds. 


mi  in  i;    1 1 « •  —  i  — . 


A-  a  result  of  the  investigations  at  Batesburg.  together  with  tin' 
earlier  observations  <>l  the  red  spider  mi  cotton,  tlii-  mite  has  been 
seen  upon  over  90  species  of  plants,  including  weeds,  ornamental 
plant-,  ami  garden  and  field  crops.  Upon  most  of  these  the  pest  has 
,inlv  occasionallv  been  seen,  '"it  it  has  been  found  commonlv  through- 


■    pica  I    *  lolel    bo 
plants  constituted  the  son  m  which  resulted  In  the  -  in  of  a 

mall  i  >otton  Beld  direct  I  j   a<  r —  the  • 

out  the  active  season  upon  the  following  plant-:  Beans,  cowpeas, 
dahlia,  ironweed,  Jerusalem-oak  weed.  Jamestown  weed,  okra,  tomato, 
wild  blackberry,  wild  geranium,  pokeweed,  and  English  violet.  \1 
Brownsville,  S.  ('..  Augusl  s.  I'.M-j.  a  case  was  seen  where  a  field  of 
corn  was  immediately  adjacenl  to  a  badly  infested  cotton  patch.  The 
infestation  had  spread  into  the  corn  and  the  cowpeas  growing  be- 
tween the  corn  rows.  One-fourth  of  the  corn  had  been  pulled  up 
ami  the  balance  was  very  severely  infested.  Many  of  the  cornstalks 
exhibited  large  rusty-yellow  blotches  on  their  blades  and,  in  fact, 
had  the  pesl  appeared  when  the  corn  was  younger  it  probably  would 
have  ruined  the  <rop.  On  the  cowpeas  the  infestation  was  heavy. 
many  of  the  leave-  had  dropped,  and  those  remaining  were  discolored 
and  distorted, 

78463      Or.  172     18 2 


THE    RED   SPIDER    ON    COTTON. 
HIBERNATION    VERSrS    WINTERING 


Some  observers  have  thought  that  the  red  spider  commonly  hiber- 
nates in  trash  or  in  the  soil  in  cotton  fields,  but  the  investigations  in 
South  Carolina  have  produced  absolutely  no  evidence  to  support  this 
idea.     During  the  late  fal]  and  early  spring,  when  the  weather  was 


Pig.  i  System  of  Besby  roots  of  the  pokeweed  (Phytolacca  decandra),  showing  the 
attractive  winter  buds  at  about  the  ground  level,  ;is  indicated  by  the  dotted  line. 
i  Original,  i 

as  cold  as  it  becomes  in  South  Carolina,  trash  has  been  taken  several 
times  from  fields  in  which  the  infestation  had  previously  been  severe 
and  examined  with  great  care.  A  few  minute  dormant  acarids  and 
other  forms  have  thus  been  obtained,  but  no  red  spiders  have  been 

found  in  such  material. 


Ill  I.    i;i  I'    SPIDI  H    ON    COTTON. 


Thai  ilii>  pesl  remains  more  or  less  active  throughout  the  winter 

there  can  be  loubt.     Mr.  <>     \.   Runner  f< I  active  adults  al 

Batesburg,  S.  C,  <>n  December  21,  1909.    Mr.  II.  I  .  Wilson  observed 
red  spiders  feeding  In  earlj  February  :ii  the  same  locality,     rhe  writei 
found  ;ill  stages  alive  on  English  violets  on  March  LI,  and  adults 
late  as  December  L9  al  Batesburg  on  the  same  host  in  1911.    Adults 
were  seen  alive  on  violets  al  Batesburg  on  February  23,  1912.  follow 
Ins  the  coldesl  winter  thai  section  had  experienced  for  mam  years. 


V.  1 

\*  5:1 

f^r                                  w 

■ 

An  uninfested  cotton  plant,  -  Id  as  shown  In  I 

beyond  the  boundnrj  of  Infestation  bj   the  red  Bplder. 

The  finding  of  the  active  red  spiders  during  the  coldesl  weather  is 
certainly  an  additional  indication  thai  hibernation  does  nol  take  place 
in  South  Carolina. 

DISPI  RSIOX. 

How  do  red  spiders  become  established  upon  cotton?  They  have 
no  wings  and  theii   legs  are  very  minute.    Cloa   observations  n 
that  on  the  ground  they  normally  travel  at  the  rate  of  1  inch  per 
L5  seconds,  which,  it'  maintained,  would  total  -lv|1  feel   in  24  hour-. 
Red  spiders  are  doubtless  occasionally  transferred  by  dogs,  chickens, 


10  THE    BED   BPIDEB   ON    COTTON. 

other  domestic  animals,  insects,  and  bird-.  Strong  winds  may  serve 
occasionally  to  transfer  them  from  plant  to  plant.  It  i-  the  writer's 
firm  belief,  however,  that  the  chief  means  of  dispersion  is  the  red 
spider's  own  efforts.  When  once  established  in  a  field  they  may  be 
further  distributed  by  farm  hands  and  by  stork  while  cultivation  is 
being  carried  on.  They  also  spread  from  plant  to  plant  along  the 
interlacing  branches,  but  trap-  specially  prepared  with  tanglefoot 
and  placed  in  the  Held  have  proven  that  individuals  commonly  crawl 
from  plant  to  plant  by  way  of  the  stalk  and  the  ground. 

Since  the  red  spider  apparently  uses  no  instinct  or  intelligence  in 
finding  cotton  plants,  it  follows  that  the  pest  must  hit  upon  the  cotton 
stalk-  entirely  by  chance.  The  result  of  this  haphazard  manner  of 
migration  must  necessarily  result  often  in  the  penetration  of  the 
spiders  far  into  the  center  of  fields,  thus  giving  rise  to  the  mistaken 
impression  that  they  had  hibernated  at  these  point-. 

Furthermore,  as  the  likelihood  of  the  discovery  of  cotton  by  the 
spider  is  doubtless  in  proportion  to  the  thickness  of  the  "  stand."  it 
should  follow  that  the  thick  broadcasting  of  a  narrow  border  strip 
along  the  edge  of  a  field  adjoining  a  source  of  infestation  would  serve 
as  a  trap  crop  to  intercept  the  majority  of  migrating  spiders.  This 
strip  should  be  plowed  in  as  soon  as  there  seems  to  be  danger  of  a 
general  movement  to  the  main  field.  (For  a  practical  test  of  this  idea, 
see  under  Prevention,  p.  17.) 

There  is  an  old  adage  which  has  come  to  the  writer's  attention 
several  times  the  past  season  from  the  lips  of  old  planters:  "When 
the  pokeweed  turns  red,  look  out  for  the  cotton  '  rust." '  This  ex- 
pression, said  to  have  been  employed  in  antebellum  days,  is  of  con- 
siderable interest,  since  it  contributes  evidence  tending  to  prove  the 
long  existence  of  the  cotton  mite  in  the  South,  as  well  as  the  function 
of  the  pokeweed. 

TIME  OF  APPEARANCE  AND  DISAPPEARANCE. 

In  1911  the  work  of  the  pest  on  cotton  first  became  noticeable  about 
June  1  at  Batesburg.  The  past  season  (1912),  however,  red-spider 
work  was  not  evident  on  cotton  until  about  the  last  of  June  at  that 
locality.  From  the  answers  to  a  large  number  of  inquiries  sent  to 
fanners  throughout  South  Carolina,  the  average  time  of  first  appear- 
ance in  fields  the  past  season  is  found  to  have  been  June  30.  The  lower 
(sandy)  section  of  the  State  averages  one-half  month  earlier  in  the 
pest's  arrival  than  does  the  upper  (clay)  section — June  2.">  marking 
the  arrival  time  for  the  former  and  July  10  for  the  latter.  Although 
the  pest  does  not  become  readily  noticeable  on  cotton  until  some  time 
in  June,  it  really  establishes  itself  considerably  earlier.  Mites  have 
•asionally  been  seen  by  the  1st  of  May  on  seedling  plants  not  over 


Ill  I     1:1  i'    -I'lhl  i;    ON    COTTON. 


11 


'_'  inches  high.     In  both    l'-'ll   and    191j2  the  pesl   abandoned  cotton 
about  the  Insl  of  August.     This  makes  the  period  of  activity   cover 

:i  I  ><  ii 1 1  12  w  ceks. 

\  \  n  1:1     •  .1     |p  \  M  m.i  . 

The  presence  of  the  pest  <>ii  cotton  is  first  revealed  by  the  appear 
a  nee  on  the  upper  surface  of  the  leaf  of  a  blood  red  spot.  A-  leaves' 
liecome  l>adl\    infested  ihe\    redden  over  tin*  entire  surface,  become 


,i.  Cross  section  of  normal  cotton  leaf;  <>.  cross  section  ol  cotton  leal  Injured 
tii.-   red    spider.     The   puncture   Is    near    lower    right-hand    corner.     Highly    magnified 
i  tatbor'a  Illustration  I 

distorted,  and  drop.  Figure  5  shows  an  uninfested  cotton  plant  for 
comparison  with  figure  7.  infested.  The  lower  have-  usually  are  first 
attacked,  but  infestation  spreads  upward  until  often  only  the  bare 
stalk  and  one  or  two  terminal  leaves  remain,  i  Sir  fig.  s.  i  Such 
plants  almost  invariably  die.  The  injury  to  the  leaf  and  the  dis- 
coloration which  follows  the  feeding  of  the  mites  are  easily  under- 
stood by  referring  to  figure  6,  winch  represents  (a)  the  appearance 
of  healthy  cotton  leaf: tissues  and  (6)  the  condition  of  the  tissue 
after  feeding  by  the  pest.  As  previously  intimated,  the  worst  spots 
of  infestation  arc  cither  to  be  found  in  close  proximity  to  yards  with 
Ixtrders  of  violets  or  to  a  clump  of  pokeweed  stalks.  Large  fields  are 
probably  never  completely  damaged,  bul  -mailer  fields  frequently 
become  wholly  affected.  A  thorough  examination  of  all  fields  within 
1  mile  of  the  center  of  Leesville.  S.  C,  was  made  with  a  view  of  detei 
mining  the  exact    status   of   red-spider   infestation   at    one   specif]  • 


12 


THE    HED   SPIDEB    <>N    COTTON. 


locality.     In  all,  99  fields  were  examined  as  carefully  as  possible. 
The  following  table  presents  the  result.-: 

Table  III. — Results  of  mi  investigation  to  determine  th<  degree  of  infestation  of 
cotton  by  the  red  spider  at  Leesville,  8.  <'..  1912. 


Number 
Degree  of  infestal  Ion      ol  fields  ex- 
amined. 

Per  cent 
of  total 
fields  ex- 
amined. 

Very  acute ix 

Very  considerable 20 

Slight 35 

None 26 

is  2 
■l- 1.  2 
35.  3 
26  3 

Total 99 

100.0 

Total  number  of  fields  visited 

Total  number  of  fields  infested ":* 

Average  percentage  of  infestation  for  the  community \.'i 


In;.  7. — Cotton  plant  in  an  early  stage  "f 
infestation  by  the  red  spider.  Many  leaves 
are  discolored  and  some  of  the  lower  ones 
have  dropped,     i  Original.  I 


p1G      s. — Cotton     plant     in     well     ad- 
vanced stage  of  infestation  by  the 
,-ed     spider.     Nearly     all     le 
squares,  and  bolls  have  been  shed. 
1 1  iriginal.  > 


This  occurrence  was  one  of  the 
at  any  time  come  to  the  writer's 
case  in  this  locality  (and  one  of 
had  its  origin  in  a  large  clump 
at   the  edge  of  town    (fig.   9). 
reached  in  one  direction  a  point 
final  affected  area,  semicircular 
within  its  confines  the  occurrence 
litis  was  unusual.  4-aav  or  5-acre 
age,  arc  frequently  to  be  seen. 


severest  and  most  general  that  has 
attention.  Perhaps  the  most  severe 
the  worst  yet  seen)  was  one  which 
of  badly  infested  pokeweed  stalks 

The  pest  spread  fanlike  until  it 
GOO  feet  from  the  pokeweed.  The 
in  shape,  comprised  13  acres,  and 
was  general.    While  such  a  case  as 

spots,  with  25  to  100  per  cent  dam- 


I  II  I     RED 


i  •  1 1 '  I  i :    O  >     i  ii I  1 1 1 N  . 


13 


NATl'RAI     '  •  i\  l  in  il  l  l  m.     \i.|  m  1 1  -. 

In  both  the  seasons  of   L911   ami   1  ■  > I _'  red  spider  occurrence  wa 

~i  severe  throughout  July  and  earlj  August.     The  last  two  week 

of  August  in  both  cases,  however,  witnessed  so  greal  n  reduction  of 
the  pesl  that  l>\  the  end  of  thai  month  il  was  hardl)  noticeable, 
:i  rule.  This  phenomenon,  indeed,  happens  suddenly,  and  the  agen 
cies  which  work  to  produce  il  are  unquestionably  of  greal  economic 
value.  The  ageing  and  toughening  of  the  leaves  al  aboul  this  time 
ni;i\  cause  many  mites  to  desert  the  cotton  for  other  plants,  but 
another  factor  of  probably  much  greater  importance  is  the  increased 
abundance  of  several  species  of  insecl  enemies  which  seem  to  gain 
dominance  nl  jusl  this  time. 


m, 

« 

A-P] 

1  •'•' 

1 

-    ■  t  - 

£**** 

•  i 

A* 

L  ?i  . 

.•» 

>-* 

i        0       \  severe  example  oJ  red-spider  work  In  a  cotton  Held      N'enrlj   all  plant*  In  the 
I  nre  In  the  i  ondll  loi  8.     1  ertaln 

I ■ . . k < - \\  •  -i  d   stnlkf 
lllnst  ration.      (Original  i 


i   MM   \  I  H'     IMI   I    I    M   1   -. 


\-  before  mentioned,  climatic  conditions  exert  a  marked  influence 
upon  the  welfare  <>f  the  pest.  During  times  of  little  rainfall  and 
high  temperature  reproduction  goes  on  h\  leaps  and  bounds;  on 
the  other  hand,  long,  heav^  rains  work  havoc  to  the  red-spider 
population.  In  spite  of  the  fad  that  the  red  spiders  inhabit  the 
underside  of  the  leaves,  many  are  washed  off  by  rains  and  many  more 
are  destroyed  by  the  upward  bombardment  of  -and  particles,  which 
may  always  be  seen  coating  the  lower  leaves  after  storms.  In  fact. 
it  appear-  true  thai  a  few  heavy  rain-,  especially  if  they  continue 
for  -mne  time,  accomplish  as  much  toward  controlling  the  pest  as 


14 


Till'.    I',K1)   BPIDEB    ON    COTTON. 


anything  which  can  1m>  done  by  man  during  the  season.  From  obser- 
vations made,  both  early  in  the  season  and  at  the  beginning  of  win- 
ter, it  is  doubtless  true  that  the  young  stages  are  killed  by  freezing 
weather.  This  naturally  prevents  any  considerable  winter  increase, 
and  in  addition  some  adults  probably  perish. 

The  influence  exerted  upon  the  red  spider  by  preseasonal  condi- 
tions appears  to  be  even  greater  than  that  of  the  factors  operating  in 
summer  weather.  The  winter  of  1J>11-12  was  the  severest  in  South 
Carolina  for  many  years.  Hence  it  might  be  expected  that  the  fol- 
lowing season  would  be  a  mild  one.  from  the  standpoint  of  injury 
l>y  the  red  spider,  through  the  assumed  heavy  mortality  of  the  pest 
during  the  winter.  On  the  contrary,  as  has  been  stated  before,  the 
1912  occurrence  was  the  severest  on  record.  The  only  possible  ex- 
planation appears  to  em- 
brace two  suppositions. 
One  is  that  the  adult  red 
spider  is  little  susceptible 
to  extreme  cold.  The 
other  is  that  the  insect 
enemies  of  the  mites  suc- 
cumb much  more  easily 
to  minimum  temperature- 
|i»  //      v~-#  than  do  the   mites  them- 

selves. Both  of  these  hy- 
potheses are  sustained  by 
all     observations     of     the 

Fig.  l&.—ArtJvrocnodai  s,,..  a  predaceous  enemy  of  writer.  .Naturally,  then,  a 
the  red  spider.  At  left,  mature  predaceous  larva,  severe  winter  is  precise! v 
magnified  60  times;  at  right,  adult  female,  greatly  1     ±  1  1  <• 

enlarged.     (Original.)  "       what     W<mld     mOS*     fav°r 

the  subsequent   increase  of 

the  red  spider  through  the  destruction  of  its  insect  enemies.  Con- 
versely, an  abnormally  mild  winter,  free  from  decidedly  low  tempera- 
tures, should  furnish  conditions  most  favorable  for  the  survival  of 
the  repressive  species,  and  the  infestation  for  the  following  season 
would  be  mild. 

INSECT     INI  MM  s. 


Hot  weather,  although  favoring  red-spider  development,  probably 
encourages  even  more  the  increase  of  insect  enemies,  of  which  sev- 
eral have  been  observed.  Were  it  not  for  these  inconspicuous  friends 
of  the  farmer  the  depredations  to  his  crops  by  the  red  spider  would 
unquestionably  be  more  severe.  The  following  are  a  few  of  the 
more  important  beneficial  species  observed  during  the  season  of  1912 
at  Batesburg,  S.  C. 


I  n  I     BED    SPIDER    ON    COTTON. 


I.". 


Wthrocnodax  sp.1   (fig.  LO).     Dunn-  the  =eae I  1912  a  species 

0f  \rthroonodnx,  a  ft}  belonging  to  the  familj  Itonida  I  formerl) 
I  ulomyiiilw).  was  first  noticed  toward  the  last  of  June,  a1  which 
"„:,,  ,,,,i  ;,i  all  common.  It  increased  wrj  rapidly,  ho* 
ever,  and  l.\  the  end  of  Juh  had  become  quite  abundant,  li  is  the 
larva  (grub  stage)  of  this  insecl  which  assists  the  farmer,  and  the 
attack  seems  to  be  limited  entirely  to  the  red-spidei  I     ming  in 

contacl   with  an  egg,  the  larva  instantly   thrusts  its  piercing  organ 
through  the  shell  and  begins  to  feed.     Large  Larva;  will  dev< 
egg   in   from  one  to  two  minutes,  while  the  smaller  larva?   require 
more  time,  according  to  their  size.     When  mature,  the  larva  spins 
a  woolh   cocoon   1   mm. 

in    length.      The    adult 

llx    issues   after  a    brief 

pupal     stage,    and     the 

full  generation  requires 

little  time.     This  insect 

i^  probabl)  the  mosl  ef 

fective  enemj  of  the  cot- 
ton mite,  and  to  its  final 

superabundance  is  prob 

:i!)l\     largely    due    the 

late  summer  decimation 

of   the    red    spider.      It 

has  been  recorded  from 

the  follow  ing  localities: 

Allendale,        Anderson, 

Batesburg,  Brownsville, 

and  St.  Matthews, S. C. ; 

Chase  City,  Va.;  Macon, 

Ga.;  and  Albertville  and  Boaz,  Ala.     It  evidently  has  a  wide  distn- 

'  TripMeps  imidiosui  Saj  (fig.  ID-  A  small  anthocorid  bug, 
Triphleps  insidi  -  s  Say,  was  seen  as  earlj  as  Maj  16.  It  is  hardier 
than  tin-  Arthrocnodas  and  appears  earlier  in  the  season.  I  hrough- 
ont  July  and  August  it  is  extremelj  common  and  both  in  the 
nymphal  and  adult  stages  is  second  only  to  the  itonid  as  a  red 
spider  enemy.     Coming  upon  a   red  spider,  like  a  flash  the  adull 

thrusts  its  sharp  proboscis  through   the   pest's  back   and   proc Is 

quietly  to  siphon  out  the  body  contents.    The  first  victim  observed 
was  "drained"  in  about  five  minutes,  but  each  succeeding  meal  was 
of  shorter  duration   as  the  appetite  became  satisfied.     The  actions 
of  the  nymph    (fig.   12)   are  similar,  but   the  individuals  obsei 
were  seen   onlv   to  destroy   eggs  of  the  spider.     In   this  operation 


Fn  .ii       /  •  ■;■■  "'    Impoi 

the    red    spld  Mu<  b    ■  VuUior's 

lllustral V 


i  The  'i  ''•  '    :'- 


16 


THE    RED    SPIDER    ON    COTTON. 


the  proboscis  was  not  inserted  far  into  the  ovum,  and  two  minutes 
sufficed  for  draining  an  egg. 

A  species  of  lace-winged  fly  {Chrysopa  quadripunctata  Burin., 
determined  by  N.  Banks)  is  abundant  at  Batesburg  throughout  most 

of  the  summer,  and  its  larva  is  doubtless  very  active  in  reducing  the 
pest. 

Two  species  of  thrips,  Euthrips  fvscus  Hinds  and  E.  occidentals 
Pergande,  have  been  determined  this  season  from  cotton.  They  arc 
commonly   found   throughout  the  season   about   red-spider  colonies, 

and  may  be  instrumental  in 
spider  destruction.  Scolo- 
f/irlps  sexmaciihitits  Pergande 
has  been  recorded  as  an  enemy 
of  the  red  spider  by  Pergande 
and  by  Duffy. 

Lady-beetle  larvae  and  adults 
of  several  species  are  com- 
monly seen  on  infested  Leaves, 
These  are  usually  either  Coc- 
cinella  9-notata  Hbst.  or  Hip- 
podamia  convergent  Giut.. 
but  a  small  black  species, 
(Scynvrms)  Stethorus  punctutn, 
Lee.  is  frequently  observed. 
The  larger  beetles  are  prob- 
ably more  intent  upon  cotton 
aphides,  but  the  last-mentioned 
species,  although  later  in  ap- 
pearing and  not  overnumerous,  seems  to  be  more  restricted  to  the 
the  cotton  mite  than  are  other  species. 


Fig.  12. — Triphleps  insidiosus:  Nymph.    Greatly 
enlarged.      (Author's  illustration.) 


REMEDIAL   MEASURES. 


PREVENTION. 


From  the  abundant  experience  of  the  past  two  years  the  writer 
has  been  forced  to  the  conclusion  that  the  eradication  of  the  red 
spider  must  be  accomplished  through  preventive  efforts  rather  than 
repressive,  if  it  is  to  be  economically  effected.  The  location  of  the 
mites  through  the  winter  and  spring,  their  preference  for  the  culti- 
vated violet  and  the  pokeweed,  and  the  manner  of  dispersion  of  the 
pest  lead  to  the  presentation  of  the  following  cultural  expedients. 

Clean  culture. — First  among  preventive  measures  against  the  red 
spider  is  doubtless  that  of  exterminating  the  weeds  and  plants  which 
breed  the  pest.  Pokeweed,  Jerusalem-oak  weed.  .Jamestown  weed, 
wild  blackberry,  and  all  border  weeds  and  underbrush  about  fields 
should  be  burned  or  grubbed  out  during  the  winter  or  early  spring. 


I  ii  E    Rl  D   BPIDEB   ON  COTTON.  17 

This  plan  has  been  tested  in  several  instances  and  has  given  complete 
illinium! \  the  following  season.  Too  much  emphasis  can  not  be 
placed  on  the  importance  of  destroying,  bo  far  as  possible,  :ill  weed 
growth  especially  the  pokeweed,  which  should  be  grubbed  out  l>\ 
the  roots. 

'  'nil  i'ii  violets.  As  before  stated,  most  cases  "f  infestation  in 
urban  localities  have  their  origin  in  borders  "I"  cultivated  violets 
growing  in  near  by  house  yards.  In  several  instances  violets  adjoin- 
ing fields  of  past  severe  annual  infestation  have  been  thoroughly 
Bprayed,  with  the  result  that  no  red  spiders  appeared  subsequently 
in  these  fields.  The  objection  to  tin-  treatment  i-  the  failure  <>n  tin 
part  of  the  average  person  to  persevere  with  the  spraying  until  the 
pests  have  been  entirely  exterminated.  The  m<>-t  satisfactory  pro 
cedure  in  such  cases  consists  in  the  removal  and  destruction  "l  the 
(  [fending  violets, 

Varietal  immunity  in  cotton.—  Prom  several  tests  conducted  in 
different  fields  with  numerous  standard  varieties  of  cotton,  and  from 
the  information  volunteered  by  farmers  from  many  portions  of 
South  Carolina,  data  have  been  accumulated  which  clearly  indicate 
that  certain  varieties  are  susceptible  t<>  red-spider  infestation,  while 
others  exhibit  considerable  immunity.  Careful  observations  on  a 
considerable  number  of  varieties  grown  for  the  purpose  showed  thai 
Dixie  "Wilt  Proof,*'  Toole,  Peterkin,  Broadwell,  and  Cook  suffer 
most  (in  the  order  named)  from  the  attack  of  the  pest,  while  Kite, 
Russell,  Summerour  "Half  and  Half,"  and  Cleveland  showed  the 
greatest  immunity  of  all  the  varieties  investigated. 

Broadcasted  cotton. — An  opportunity  was  accidentally  provided  of 
testing  the  value  of  thickly  broadcasting  cotton  ;it  the  boundary  of 
;i  field  as  ;i  trap  crop  for  red  spiders.  This  cotton,  intended  as  ;i 
cover  crop,  intervened  between  the  cotton  field  proper  and  a  large, 
heavily  infested  border  of  violets  -a  former  abundant  source  of 
migration.  The  broadcasted  cotton  became  infested  and  was  later 
plowed  in.  The  adjoining  field  remained  free  from  mites.  The  suc- 
cess of  this  experiment  would  strongly  indicate  that  the  cotton  trap 
crop  i-  a  practical  cultural  expedient  to  be  used  in  controlling  tin- 

pe-t. 

Spacing.— Experiments  at  Batesburg,  S.  C,  have  shown  that  the 
red  spider  commonly  travels  between  plant-  upon  the  ground.  This 
-how-  the  futility  of  spacing  as  a  remedial  measure. 

Thm    of  planting.      There  i-  yet   much  doubl   as  to  the  relative  ad- 

vantages  of  early  and  late  planting.  Extremely  early  planting  nat 
urally  permit-  the  plant-  to  develop  a  maximum  growth  of  weed 
and  fruit  by  the  time  of  serious  mite  appearance.  It  is  noticeable 
that  plant-  of  considerable  size  are  rarely  hilled  by  the  pe-t.  nor  are 
well-advanced  bolls  commonly  shed  from  infestation.  On  the  other 
hand,  several  field-  about   Leesville,  S.  (\.  which  were  planted 


18  THE   RED   SPIDER   OX    COTTON. 

late  as  June  20  seem  to  have  largely  escaped  the  infestation  which 
was  so  general  at  that  locality.  Late  planting,  however,  is  almost 
universally  objectionable  to  the  farmer,  since  in  ordinary  seasons  it 
results  in  a  reduction  of  the  yield. 

Rotation. —  In  an  effort  to  test  the  rotational  value  of  other  crops, 
numerous  field  crops  have  been  planted  in  or  near  infested  areas. 
In  addition,  frequent  examinations  have  been  made  of  a  great  many 
garden  and  vegetable  crop-  in  infested  localities.  Besides  cotton. 
red  spiders  are  known  to  occur  not  at  all  uncommonly  upon  the  fol- 
lowing field  crops:  Cowpeas,  clover,  corn.  hops,  and  watermelon. 
They  are  also  found  frequently  on  the  following  garden  crops:  Peas. 
beans,  onion,  tomato,  lettuce,  okra.  turnip,  mustard,  squash,  beet, 
sweet  potato,  and  strawberry.  A  really  acute  infestation  on  corn 
(as  above  recorded)  was  seen  at  the  height  of  the  past  season  (1912). 
Cowpeas  are  particularly  attractive  to  the  pest,  and  sweet  potatoes 
have  been  noted  to  be  badly  infested.  Should  an  immune  crop  be 
found  and  employed,  it  is  extremely  probable  that  the  pest  would 
reinvade  the  fields  upon  the  return  to  cotton  culture  with  as  great 
ease  and  quickness  as  it  has  done  during  any  previous  season,  provid- 
ing the  sources  of  infestation  were  yet  at  hand.  Rotation,  then,  does 
not  promise  to  contribute  toward  the  solution  of  the  problem. 

Effects  of  fertilizers. — A  rather  elaborate  series  of  tests  with  fer- 
tilizers has  been  conducted  in  an  attempt  to  determine  whether  the 
various  applications  assisted  cotton  to  withstand  the  injurious  effects 
of  infestation.  Since  almost  no  infestation  appeared  in  these  test 
plats  it  was  impossible  to  deduce  positive  conclusions. 

REPRESSION. 

We  have  just  discussed  cultural  measures  which  may  help  to  pre- 
vent infestation.  We  will  now  consider  what  may  be  done  to  combat 
the  pest  when  it  has  already  gained  entrance  to  a  Held. 

The  writer  believes  in  prevention  rather  than  cure,  in  the  case  of 
the  red  spider.  When  once  well  established  in  a  cotton  Held  the 
pest  is  a  most  difficult  one  to  wipe  out.  That  it  is  possible,  however, 
to  eradicate  the  pest  from  infested  fields  has  been  demonstrated  be- 
yond  doubt,  but  in  many  cases  the  task  i-  so  tedious  that  only  the 
most  determined  farmers  will  undergo  the  effort  necessary  to  accom- 
plish the  extermination. 

ll<  moral  of  infested  plants. — The  experiment  ha-  been  thoroughly 
tested  of  pulling  up  ami  destroying  the  Hist  few  plant-  which  show 
infestation.  In  such  cases  the  operation  was  repeated  several  times. 
Great  care  was  observed  in  locating  every  plant  showing  the  charac- 
teristic red  spots,  and  these  were  carefully  taken  from  the  Held  and 
burned.  If  infestation  has  not  advanced  far.  this  treatment  is 
usually  satisfactory,  and  a  red-spider  invasion  often  may  be  "  nipped 
in  the  bud  "  and  entirely  eradicated. 


Mil     RED    -rihi  i:    ON    COTTON. 


19 


[f  infestation  has  spread  until  a  considerable  patch  has  become 
involved  ii  is  Bometimes  advisable,  in  the  case  "I"  a  large  field,  t"  plow 
up  nil  the  affected  portion  in  order  i"  Bave  the  balance  of  the  field. 
Such  ;i  drastic  measure,  however,  should  orilj  be  resorted  to  in  es 
treme  cases,  and   the  planter  concerned   must   l>e  the   j 1 1 « I i-r * •  oi 
;nl\  isability. 

Occasional  observations  <>l"  instances  wherein  infestation  had 
abruptly  stopped  ;it  ;i  much-traveled  road  suggested  the  idea  of  plow- 
ing a  wide  swath  just  outside  the  boundary  of  infestation.  This 
attempted  in  one  case  where  the  occurrence  had  covered  aboiil  2 
acres.  A  LO  fool  ring  was  plowed  around  the  spot,  and  all  stalks, 
both  in  the  swath  and  in  the  inclosed  area,  were  immediately  burned. 
Unfortunately  the  farmer  did  n<»i  make  sure  thai  he  was  beyond  the 
outermost  /.one  of  infestation,  and  consequently  ;i  sufficient  number 
of  affected  plants  remained  outside  the  pulverized  barrier  to  con- 
tinue, somewhat,  the  dispersion  of  the  pest.  This  idea  should  be 
given  further  tests,  as  it  seems  there  should  be  great  efficacy  in  the 
operation,  provided  the  swath  i-  kepi  stirred  frequently. 

Insecticides.  During  the  season  <>f  L911,  26  spraj  combinations 
were  thoroughly  tested  under  conditions  entirely  natural.  The  field 
used  for  this  purpose  was  aboul  1  acre  in  extent,  and  infestation  had 
become  both  very  genera]  and  very  severe.  A  strip  through  the  mid- 
dle of  the  field,  crossing  each  sprayed  plat,  was  lefl  unsprayed  t<> 
serve  as  m  check.  Since  do  substance  was  discovered  which  could  be 
safely  used  to  destroy  all  eggs  in  one  application,  it  was  found  nei 
sary  t<>  spray  twice,  with  an  interval  of  six  or  se1  en  days,  so  as  t"  de- 
stroy tlu>  hatching  larva;.  The  killing  ability  of  all  these  sprays  was 
computed,  and  the  percentages  ranged  from  I1111  to  0.  Each  of  the 
following  six  combinations  (see  Table  IV)  was  found  to  be  very 
satisfactory.  These  are  presented  to  indicate  the  manner  of  prepara- 
tion, together  with  the  cost,  of  LOO  gallons  <d"  each. 

TABl       I  \  ■tins!    th(  /<  /■. 


i 
ii 

in 

IV 
V 

VI 


lions. 
Flowers  of  sulphur  | 

timi  ...|  I 

" 

" 

Blacklral  tol  .unccs,  at  * 

:;  ! 
•■  U)  111  l^''  101  

Flowers  of  sulphur.  X  .  $1.12 

per  pourj  i 
Water  to  m  


JO  75 


1   40 


100 
100 


- 


20  THE    RED   SPIDER   OX   COTTON. 

In  the  course  of  spraying  tests  against  the  red  spider  on  hops  in 
California,  conducted  by  Mr.  W.  B.  Parker.1  of  thi-  bureau,  it  seems 
to  have  been  demonstrated  that  Hour  paste,  used  alone  or  combined 
with  caustic  materials,  is  a  valuable  acaricide.  The  function  of  the 
flour  paste  appears  to  be  twofold:  Used  alone  it  glues  the  tiny  mites 
to  the  leaves,  and  when  added  to  lime-sulphur,  or  other  solutions,  it 
serves  as  a  spreader  to  prevent  the  spray  film  from  breaking  up  into 
"•  I  icads  "  as  it  dries  on  the  leaf.  Mr.  Parker  recommends  the  follow- 
ing formulas : 

I.  Stock  solution  of  flour  paste. 

Mix  cheap  wheat  flour  with  cold  water  at  the  rate  of  1  pound  of  flour 
to  1  gallon  of  water.     Boil  to  a  paste. 
II.  Flour-paste  spray. 

Use  8  gallons  of  the  above  stock-solution  paste  to  each  100  gallons  of 
water.     Keep  constantly  agitated  while  spraying. 
III.  lime-sulphur  and  flour-paste  mixture. 

Use  4  gallons  of  flour-paste  stock  solution  to  each  loo  gallons  of  lirne- 
sulphur  spray. 

During  the  recent  season  no  serious  effort  was  made  to  test  addi- 
tional insecticides.  Further  use  of  the  sprays  mentioned,  however, 
seems  to  establish  the  superiority  of  potassium  sulphid,  lime-sulphur 
solution,  and  miscible-oil-tobacco  solution.  The  last  preparation 
seems  to  possess  better  lasting  qualities  than  the  others,  since,  in  the 
absence  of  rain,  one  application  will  also  suffice  to  kill  a  certain  per- 
centage of  the  hatching  larva?.  If  one  of  these  were  to  be  used  in 
preference  to  all  others,  it  would  probably  be  potassium  sulphid. 
This  insecticide  commends  itself  from  every  standpoint — cheapness, 
simplicity  of  preparation,  ability  to  kill  quickly,  and  safety  of  foliage. 
Altogether  it  seems  to  be  an  ideal  red-spider  spray.  It  was  found 
that  100  gallons,  wdien  applied  as  a  mist  spray,  about  sufficed  to  treat 
an  acre  of  average-sized  cotton. 

Spraying  out-fits. — The  sort  of  outfit  to  be  used  for  red-.-pider 
s{3raying  depends  mainly  upon  the  extent  of  the  occurrence.  Some 
have  sprayed  their  score  or  so  of  affected  plants  with  a  75-cent  tin 
atomizer.  While  this  instrument  is  very  economical  of  liquid  and 
throws  a  misty  spray  which  penetrates  and  blows  to  all  parts,  it  is 
not  economical  of  time.  The  bucket  pump  and  knapsack  pump  come 
into  use  in  cases  of  considerable  scattered  infestation  or  for  the 
treatment  of  a  few  high  plants.  The  most  economic  outfit  for  a 
severe  case  involving  several  acres  consists  of  a  barrel  pump  carried 
through  the  field  on  a  wagon.  One  man  drives,  one  pumps,  and  one 
handles  each  sprayer  (of  which  preferably  there  should  be  two). 
Thorough  treatment  of  3  or  -1  acres  per  day  is  readily  obtainable  with 
this  device.    For  safe  work,  however,  this  outfit  should  1m?  used  only 

1  Flour  pnstp  as  a  control  for  red  spiders  and  as  a  spreader  for  contact  insecticides, 
Clr.  IOC.  Bur.  Ent,  T".  S.  Dept.  Agr.,  January  30,  1913;  The  rod  spider  on  hops  in  the 
Sacramento  Valley  of  California,  Bui.  11",  Bur.  Ent.,  D.  S.  Dept.  Agr.,  1913. 


Ill  B    BSD   BPIDBB   ON  COTTON.  2  1 

on  cotton  of  average  or  loti  Bize,  as  the  passing  wagon  will  injure 
large  plants. 

\  ' i/  for  thorough  spraying.     Some  dissatisfaction  has  been 

experienced  among  certain  of  those  who  have  undertaken  to  check 
the  ravages  of  the  red  spider  l>\  spraying.  This  can  be  understood 
on  account  of  the  extreme  care  which  must  be  exercised  in  order  to 
secure  effective  results.  In  the  case  of  insects  which  devour  the  plant 
tissue  even  the  careless  application  of  Paris  green  or  lead  arsenate  to 
the  top  of  the  foliage  is  often  effective.  Tin-  is  explained  by  the  fact 
that  such  pests  are  constantly  moving  from  leaf  t"  leaf  and  will 
eventually  eat  some  of  the  poisoned  tissue.  Moreover,  these  insects 
often  eat  entirely  through  the  leaf,  and  In 'net'  it  mat  in--  little  whether 
the  poison  falls  upon  one  side  or  the  other.  With  the  red  spider, 
however,  it  is  altogether  different.  A  contact  insecticide  is  absolutely 
necessary,  and,  from  the  fact  that  the  mite  as  a  rule  passes  it-  entire 
existence  upon  the  underside  of  a  single  leaf,  it  becomes  plainly 
necessary  in  spraying  to  hit  tin  entire  undersidi  of  <  very  l<'ii  of  an 
infested  plant.  It  is  obvious,  therefore,  thai  indifferent  spraying  is 
certain  t<>  yield  unsatisfactory  results.  Furthermore,  the  absolute 
necessity  for  a  second  spraying  to  kill  the  hatched  eggs  add-  to  the 
difficulty. 

It  i-  hoped  that  this  discussion  may  impress  upon  the  reader  tin 
•  i<r-  r,  ntion  of  iii  festal  ion. 

-t   mm  w:>  . 

The  female  red  spider,  appearing  to  the  naked  eye  like  a  dot  of 
reddish  ink  from  the  point  of  a  fine  pen,  lays  about  50  or  60  round, 
colorless  eggs,  which  hatch  in  summer  time  in  about  four  day-. 

The  colorless,  newborn  spider  has  six  legs,  \'rv<\^  at  once,  and  molts 
in  two  day-  to  the  primary  nymph. 

This  first  nymphal  stage  (and  all  later  stages)  possesses  eight  legs, 
and  ha>  become  larger  in  size  and  darker  in  color.  In  two  more  days 
t  in  summer)  it.  in  turn,  molts  to  the  secondary  nymph. 

The  second  nymphal  stage  lasts  two  day-,  at  the  end  of  which  time, 
after  molting,  the  fully  formed  adult  emerges.  Mating  occur-  at 
once  and  egg  laying  commences  immediately  afterward-. 

Thus  one  generation  requires  in  summer  weather  in  South  Caro- 
lina about  K>  or  11  day-.  There  are  probably  about  16  or  17  genera- 
tions in  an  average  year  iii  that  locality. 

The  red-spider  colonies  live  on  the  underside  of  the  cotton  leaves, 
and  their  constant  feeding  causes  hlood-red  spots  to  appear  on  the 
top-  of  the  leave.-.  The  effect  upon  the  cotton  plant  is  that  the  leaves 
drop,  one  by  one.  until  usually  the  plant   •lie-. 

The  pe-t  increases  and  spreads  most  rapidly  in  hot.  dry  weather 
until  (toward  the  end  id'  August  I  -evcral  acre-  of  a  field  may  become 
badly  damaged. 


UNIVERSITY  OF  FLORIDA 


22 


THE    BED   SF1DBB   OH    C<  ,j|,l!J^ll2i  'S^^'e""/^^ 

Several  insects  have  been  discovered  which  destroy  many  mites 
and  are  thus  of  great  benefit  to  the  planter. 

At  the  end  of  the  cotton-growing  season  most  of  the  red  spiders 
migrate  afool  in  search  of  greener  plants.  The  majority  of  those 
which  arc  destined  to  survive  the  winter  probably  settle  on  either  the 
cultivated  violet  or  on  the  pokeweed. 

RECOMMENDATIONS. 

(/)  Clean  culture.— Destroy,  by  burning  and  grubbing  out,  all 
weed,  and  underbrush  about  cotton  fields,  being  especially  careful  to 
remove  all  pokeweed.      Practice  fail  plowing  so  far  as  possible, 

(2)  Control  on  violets.— Destroy  or  thoroughly  spray  cultivated 
violet  plants  which  may  he  growing  near  cotton  field-. 

(S)  Resistant  varieties. — In  choosing  seed  for  the  crop  avoid  varie- 
ties which  suffer  most  from  red-spider  attack. 

( .',)  Broadcasted  trap  borders. — Thickly  sow  cotton  along  margins 
of  fields  at  points  where  infestation  has  appeared  on  former  occasions 
and  plow  these  in  about  dime  1.  so  as  to  intercept  and  destroy  the  in- 
vading mites. 

(5)  Putting  -first  infested  stalks.— Maintain  a  careful  watch  of 
fields  from  the  time  of  the  earliest  appearance  of  cotton  above  ground, 
so  that  the  first  attacked  plant-  may  he  detected,  removed,  and  burned, 
thus  preventing  further  spread. 

{6)  Barrier  strip.— In  case  a  considerable  area  of  cotton  has  be- 
come affected  before  discovery,  remove  and  burn  the  worst  of  it  and 
then  plow  a  10- foot  -trip  completely  around  the  extreme  outside  of 
the  infested  area.  Keep  this  strip  stirred  frequently  to  make  further 
dispersion  difficult. 

(7)  Spraying.— Apply  one  of  the  insecticides  recommended  to  the 
infested  portion  of  a  field  before  infestation  becomes  too  general  to 
prohibit  its  use.  Choose  the  pump  outfit  which  hot  suits  the  par- 
ticular case.  Two  application-  should  be  made.  The  second,  a  week- 
after  the  hist,  i-  to  kill  the  individuals  which  were  eggs  at  the  time  of 
the  first  spraying. 

Unlike  many  other  pests,  the  red  spider  has  no  wings  and  spreads 
mainly  by  means  of  its  tiny  legs.  Migration  doe-  not  extend  far  from 
its  winter  quarters.  This  makes  every  man'.-  problem  virtually  his 
own.  In  other  word-,  if  his  infestation  always  come-  from  a  certain 
spot  upon  his  premises,  proper  attention  to  this  -pot  will  yield  him 
satisfactory  results  in  spite  of  the  negligence  of  hi-  neighbors. 

Approved  : 

Jambs  Wilson, 

Secretary  of  Agriculture. 
Washington,  I).  C.  January  ..'.J.  WIS. 

O 


